This application is based on Japanese Patent Application 2000-173244, filed on Jun. 9, 2000, the entire contents of which are incorporated herein by reference.
a) Field of the Invention
The present invention relates to a laser processing apparatus and method, and more particularly to a laser processing apparatus and method for applying a pulse laser beam having a wavelength in an ultraviolet range to a workpiece and forming a hole in or through the workpiece.
b) Description of the Related Art
A conventional laser processing method will be described by taking as an example a method of forming a hole in or through a multi-layer wiring substrate. An infrared pulse laser beam radiated from a carbon dioxide gas laser oscillator is converged at a resin layer of a multi-layer wiring substrate. Organic substance in the region applied with the laser beam is thermally decomposed and a hole is formed in this region. With this method, a through hole 100 to 200 xcexcm in diameter can be formed through a resin layer about 40 to 80 xcexcm thick. A carbon dioxide gas laser oscillator can radiate a pulse laser beam having a high energy per one pulse. This pulse laser beam can form a through hole, for example, by three shots.
Holes having shorter diameters are desired to be formed in a multi-layer wiring substrate of a semiconductor integrated circuit device which is implemented at a higher integration density. A lower limit of the diameter of a hole is about five times the wavelength of a laser beam used. If a carbon dioxide laser is used, the lower limit of a hole is about 50 xcexcm. It is practically difficult to form a hole having a diameter smaller than 50 to 60 xcexcm by using a carbon dioxide gas laser.
If a laser beam having a wavelength in the ultraviolet range is used, a hole having a smaller diameter can be formed. It is difficult, however, to generate a laser beam having a wavelength in the ultraviolet range and a large power. If a laser beam having a small power is used for processing a multi-layer wiring substrate, a process time prolongs and productivity lowers.
It is an object of the present invention to provide a laser processing apparatus and method capable of shortening a process time by using a laser beam having a wavelength in the ultraviolet range.
According to one aspect of the present invention, there is provided a laser processing apparatus comprising: controller for outputting a first event signal having a periodical waveform and a second event signal having a periodical waveform synchronizing with the first event signal; a first laser source for radiating a first pulse laser beam having a wavelength in an ultraviolet range, synchronously with the first event signal; a second laser source for radiating a second pulse laser beam having a wavelength in the ultraviolet range, synchronously with the second event signal; a converging optical system for converging the first and second pulse laser beams at a same point; and holder for holding a workpiece at a position where a pulse laser beam converged by the converging optical system is applied.
According to another aspect of the present invention, there is provided a laser processing method comprising the steps of: radiating a first pulse laser beam from a first laser source, the first pulse laser beam having a wavelength in an ultraviolet range; radiating a second pulse laser beam from a second laser source synchronously with the first pulse laser beam, the second pulse laser beam having a wavelength in the ultraviolet range; and applying the first and second pulse laser beams to a same processing area of a workpiece to form a hole in the same processing area.
When the pulses of the first and second pulse laser beams are alternately applied to the same point of a workpiece, a process speed can be approximately doubled. When the pulses of the first and second pulse laser beams are overlapped, the energy per one pulse can be increased so that a workpiece can be processed which requires a large energy for forming a hole.
According to another aspect of the present invention, there is provided a laser processing method comprising the steps of: preparing a workpiece having a first layer and a second layer formed under the first layer, wherein a hole can be formed in the first layer by applying an ultraviolet pulse laser beam having a first energy per one pulse, and a hole can be formed in the second layer by applying an ultraviolet pulse laser beam having not the first energy per one pulse but a second energy per one pulse higher than the first energy; applying a first pulse laser beam and a second pulse laser beam to the first layer in a processing area thereof under a timing condition that pulses of the first and second pulse laser beams are alternately applied to the first layer, to form a first hole in the first layer and expose a partial surface of the second layer under the first layer, the first pulse laser beam being radiated from a first laser source and having a wavelength in an ultraviolet range, and the second pulse laser beam being radiated from a second laser source and having a wavelength in the ultraviolet range; and applying the first and second pulse laser beams to the second layer exposed on a bottom of the first hole under a timing condition that pulses of the first and second pulse laser beams are at least partially overlapped, to form a second hole in the second layer, the first pulse laser beam being radiated from the first laser source and having the wavelength in the ultraviolet range, and the second pulse laser beam being radiated from the second laser source and having the wavelength in the ultraviolet range.
By chanting the timing conditions of the first and second pulse laser beams, the first and second layers can be processed continuously.
According to another aspect of the present invention, there is provided a laser processing apparatus comprising: controller for outputting a first event signal having a periodical waveform and a second event signal having a periodical waveform synchronizing with the first event signal; a first laser source for radiating a first pulse laser beam having a wavelength in an infrared or visual range, synchronously with the first event signal; a second laser source for radiating a second pulse laser beam having a wavelength in the infrared or visual range, synchronously with the second event signal; an optical propagation system for changing an optical axis of at least one of the first and second laser beams so as to make the first and second pulse laser beams propagate along a same optical axis; a non-linear optical component for generating a harmonic wave having a wavelength in an ultraviolet range, from the first and second pulse laser beams made to have the same optical axis by the optical propagation system; a converging optical system for converging the harmonic wave; and holder for holding a workpiece at a position where the harmonic wave converged by the converging optical system is applied.
As the pulses of the first and second pulse laser beams alternately reach the non-linear optical component, a harmonic wave is generated having a repetition frequency twice as high as the repetition frequency of each of the input pulse laser beams. A process time can therefore be shortened. When the pulses of the first and second pulse laser beams are overlapped and become incident upon the non-linear optical component, the energy per one pulse of the harmonic wave increases so that a workpiece can be processed which requires a large energy for forming a hole.
As above, by combining the pulse laser beams radiated from the two laser sources to have a predetermined phase difference, the hole forming time can be shortened. By overlapping the pulses of the first and second pulse laser beams, the energy per one pulse can be increased. Even if a sufficient energy per one pulse cannot be obtained by one laser source, a sufficient energy can be obtained by using two laser sources. A hole can be formed in a workpiece even if it requires a large energy per one pulse.